Alterations in regional perfusion have been demonstrated with x-ray transmission computed tomography (CT). A continuously rotating CT scanner will be used to generate electrocardiographic (ECG) gated and dynamic images of the myocardium using specially developed computer programs designed to improve the temporal resolution of the image. Dogs with normal, ischemic, and infarcted hearts will be studied using ECG-gated and dynamic CT, and estimates of regional myocardial perfusion will be obtained by measuring the mean transit-time of iodinated contrast material as it passes through the myocardium. Simultaneous measurements of regional coronary blood flow using radiolabelled microspheres will provide correlation with CT estimates of perfusion. It is expected that the accurate spatial and density resolution of computed tomography will significantly improve the detectibility of myocardial ischemia and infarction compared with existing techniques.